The present invention relates generally to shock-absorbing structures, more particularly, to safety features incorporated into vehicle seats such as those found in aircraft, to protect the occupant, insofar as it is possible, from shock induced injury. Such structures may find utility in related fields such as automotive, machinery, or any vehicle having human occupants.
Vehicles are generally operated by human operators in a seated position within the vehicle. Such vehicles include land based vehicles such as automobiles, trucks, earth moving equipment, and the like; sea based vehicles such as boats and submarines; and flying vehicles such as aircraft, helicopters, and spacecraft. Because the vehicle is generally in motion, external forces may cause the compartment to abruptly change its direction of motion, resulting in forces exerted upon the occupant. These forces are made up of a horizontally oriented component and a vertically oriented component. The horizontal component may generally be handled by the use of seatbelts and padded structures.
The vertical force component may present characteristics that cannot be handled by seatbelts and padded structures. Given that the occupant is in a normal seated position, such vertical forces might be caused by a vertical fall ending in an abrupt stop. Seats have been fabricated with innovative cushions, springs, and hydraulic shock absorbers, all installed in the base of the seat, to dissipate such sudden and short duration vertical forces. Some of devices exhibit the tendency to return to the original configuration after dissipating the force, and other devices permanently deform to absorb the force and thus must be replaced afterwards.
Aircraft crash impacts in general, and helicopter crash impacts in particular, can produce decelerations in excess of 50 g. Without attenuation, these forces can result in serious injury or death to the occupants. Although a wide range of energy-absorbing seat designs are available, they have a number of deficiencies. First, such designs in general are mechanically complex. Second, their complexity tends to make such seating arrangements more expensive than normal seating arrangements. Third, mechanically complex designs tend to be heavy, which can be a serious disadvantage in aircraft where low weight is a desirable characteristic. Fourth, mechanically complex designs tend to be bulky, which can also be a serious disadvantage in aircraft where space is at a premium. Finally, designs that are mechanically complex, heavy, and bulky have been shown through to experience to have more expensive life cycle costs, in terms of repair, training, replacement parts, inventory, training for repair personnel, and so forth.
Most existing airborne vehicles are equipped with seating arrangements that cannot absorb sufficient impact energy or attenuate impact forces to prevent serious injury to the occupants. Incorporating better seating structures into new or in-service vehicles can degrade performance by increasing weight of the vehicle, where the weight penalty increases as the number of affected seats increases. Furthermore, replacing existing seating arrangements results in increased acquisition and maintenance costs. Any attempt to retrofit complex and bulky energy absorbing seats into existing airborne vehicles can be thus be both problematic and impractical.
The difficulty in retrofitting seat into existing aircraft exists throughout the complete spectrum of military and commercial helicopters and aircraft. Some commercial aircraft and helicopters must be certified according to the United Stated Consolidated Federal Regulations (CFR) 124, Parts 23, 25, 27, and 29, which requires impact testing of seats. This requirement was added long after most of the existing fleets had been produced. For the most part, these existing seats are therefore not compliant with the current requirements. To aggravate the problem, aircraft and helicopters certified to the earlier and less stringent regulations may continue to be produced under a “grandfather clause” without being required to meet these new regulations.
The inventor's U.S. Pat. No. 6,561,580, entitled “Energy Absorbing Seat”, issued on May 13, 2003, provides such an inexpensive, lightweight seating apparatus and is incorporated herein by reference in its entirety. It provides a seating pan structure that is constructed of expanded metal and can be easily retrofitted into existing seating arrangements without extensive modification. The structure has sufficient elasticity to maintain its shape when subjected to moderate amounts of force. When subjected to a high level of vertical force, the seating pan structure deforms elasto-plastically to absorb a significant amount of the vertical force, so that injury to the lumbar area of the person occupying the seat is either eliminated or greatly reduced. However, over long periods of use, the structure can experience a series of small amounts of vertical force that can slightly exceed the elastic limit of the material and gradually deform it over time. The cumulative effect of successive slight deformations may result in periodic replacement of the seating pan structure.
As can be seen, there is a need for a seating apparatus for a person in a vehicle that is subject to vertical impact loads and where the seating apparatus is configured to attenuate such vertical forces without undue detrimental affect on the person occupying the seat. The seating apparatus should be simple in construction and therefore inexpensive. It should also be light and compact so that it is suitable for retrofit applications. Finally, the seating apparatus should be sufficiently resistant to the cumulative effect of non-catastrophic vertical loads so as to reduce the likelihood of deformation during normal use.